Inventors have surprisingly discovered inhibitor peptides that can be used to block nuclear translocation of EGFR. In some embodiments, the inhibitor peptides of the present invention can be used for combinatorial inactivation of EGFR (ErbB1), ErbB2, and ErbB3. The inhibitor peptides comprise an EGFR-based peptide, which is related to the EGFR juxtamembrane region. In some embodiments, the EGFR-based peptide comprises the tri-partite nuclear localization sequence of EGFR, which can act in a dominant-negative fashion to block nuclear translocation of EGFR. In some embodiments, the EGFR-based peptide is fused to (directly or indirectly) or synthesized in tandem with a cell penetrating component for cellular uptake (e.g., a protein transduction domain, e.g., PTD-4). One such inhibitor peptide, ENLS-1 (SEQ ID NO: 13, see FIG. 1) has been tested for its ability to block breast cancer cell growth and tumor growth in a transgenic mouse model, MMTV-pyMT. Other peptides also have been tested and found to have cell growth inhibitory properties (see FIG. 1).